Ethanol-water clusters determine the critical concentration of alcoholic beverages

Abstract

Alcoholic beverages are conventionally classified by alcohol by volume (ABV) based on ethanol-water mixture (EWM) concentrations, which is regarded as empirical with little scientific explanation. Here, we find that contact angles of EWMs with different ethanol fractions on highly oriented pyrolytic graphite are non-linear but steplike, while the critical points at step edges surprisingly fit the distributions of ABV. High-frequency proton nuclear magnetic resonance and molecular dynamics confirm different ethanol-water clusters in EWMs, whose structures undergo transitions at the critical points and keep stable in step ranges. Detailed cluster structures contain symmetric tetrahedral and chain-like clusters, and the ratio of the latter increases with higher ethanol fraction, further characterized by attenuated total reflectance infrared spectroscopy. Influence of temperature on clusters probably accounts for preferable changes of “ethanol-like tastes” of low-ABV beers or white wine after cooling and high-ABV shochu or Chinese baijiu after heating.